Epitaxial growth and characterization of semiconducting materials and nanostructures

TeamMatteo Bosi

Claudio FerrariPaola FrigeriEnos GombiaLuca Seravalli

Giovanna Trevisi

ActivitiesSynthesis and study of semiconducting materials and nanostructuresModelling of electronic properties of quantum confined systems

Developing new tools and methods for structural and electrical characterization

Scientific areas of interest:Structures tailored to sensing: nanowires, quantum dot, microtubes, MEMSMaterial for photonicsMaterial for power devices

SkillsEpitaxial growth (MOVPE, ALD, MBE)

Materials: Ge, Ga2O3, SiC, III‐VCharacterization of semiconductors and nanostructures:

Morphological (SEM, AFM)Structural (XRD)Optical (PL, transmission, reflectance)Electrical

Micro/nano fabrication by focused ion beam PhotolitographyDesign / modeling of quantum, nano and photonic structures

UdR “Growin”

UdR “Growin”

Overview of the main facilities:

2x MOVPEMBEXRD systems (high resolution, 2D detector)Clean room with laminar hood for chemical preparationPhotoluminescence, transmittance, reflectanceElectrical characterizationTiberCAD software for nanostructures modelling

UdR “Growin”

Main facilities:MOVPE (1)

Designed for 3C‐SiC / Si epitaxyNow used to grow Ge and Si nanowires

max T 1500 °Cmin P 100 mbarH2, Ar atmosphereSubstrate area 2x4 cm2

Sources:2 main gas lines ‐ SiH4, C3H82x metal organic lines ‐ Ge, Ga, Al, As, P, Zn, Indisposable cylinders (12L, 1bar)  ‐ N2, C2H4, C2H6

UdR “Growin”

Main facilities:MOVPE / ALD (2)

Designed for oxides / ALD is possibleNow used to grow Ga2O3

max T 600 °Cmin P 100 mbarH2, N2 atmospheresubstrate area: 2’’

Sources:1 main gas line ‐ SiH43x metal organic lines – Ga, H2O, Ti, Al

UdR “Growin”

Main facilities:MOVPE / ALD (2)

In the past: Al2O3 and TiO2 layers by ALD

… but ALD had some technical problemsHardware upgrade is necessary for development

Conformal 

Conformal deposition of high aspect‐ratio structuresPrecise control of thickness / n° of layers

UdR “Growin”

Main facilities:MBE Equipment

Group III (Ga, In, Al) effusion cellsAs valved cracker cellSi, Be doping sourcesIn‐situ diagnostic: RHEEDClean room (class 100 and class 10000)

Present situationGrowth activity suffers from technical problemsand lack of adequate fundings

The MBE growth techniques allows for the depositionof thin layers of semiconducting materials with highcrystal quality, reduced incorporation of undesiredimpurities, controlled doping and compositionprofiles along the growth direction, atomic‐scalesmoothness of the interfaces.

UdR “Growin”

Main facilities:Optical characterization

Photoluminescence Spectroscopy, Reflectance, Transmittance532 nm laser10 ‐ 300 K Fourier transform spectrometerLiquid N2 Cooled Ge Detector

Electrical characterizationElectrical measurements (10‐330 K)Preparation of Ohmic and Schottky contacts by thermal evaporation and annealing I‐V, C‐V, Deep Levels Transient Spectroscopy, Admittance Spectroscopy

UdR “Growin”

Main facilities:Tiber CAD – modelling software

Software tool for numerical simulation of electronic and optoelectronic devicesModelling and design of nanostructured devices 

e.g.: III/V LEDs, nanowire FETs, Dye Solar CellsAtomistic and continuous finite element method models availableExtensive material database: zincblend and wurtzite, ternary and quaternary alloys1D/2D/3D modeling and meshing, cylindrical symmetryAvailable modules:

thermalelasticitydrift‐diffusionenvelope function approximation

UdR “Growin”

Main facilities:Structural characterization by X‐Ray Diffraction

High resolution XRD Panalytical Xpert‐Pro with Goebel mirror and crystal analalyser: reciprocal lattice maps in high or medium angular resolution and x‐ray  polar maps

XRD with Goebel mirror for powder monochromatic diffraction and thin film characterizationDouble crystal x‐ray topography camera for large crystal charcateriztion

-3.3 -3.2 -3.1 -3 -2.9

4.35

4.4

4.45

4.5

4.55

4.6

4.65

4.7

kx (1/Å)

ky (1

/Å)

Si1455m3

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Si 422 peak

Ge 422 peak

Strained422 SiGeLayer peak

n̂

NATO Science for Peace program – grant SPS G5423 (2018 – 2020)“Portable sensors for unmanned explosive detection” (P.I. : Claudio Ferrari)

Participants:  IMEMChemistry dept. UniPRAzerbaijian National Academy of Sciences

Funding

Partner Countries  140.000

NATO countries (Azerbaijian) 200.000

Total (3y) 340.000

Aims Preparation of explosive sensors based on functionalized semiconductor nanowires or carbon nanotubes Very limited mass, power consumption and dimension. Tailored for installation in an unmanned drone

NATO Science for Peace – nanostructures for explosive detection

Semiconducting nanowiresGe as a “new” semiconducting material for (nano)devices:

direct bandgap=0.8 eVindirect bandgap=0.66 eVhigher carrier mobilitylarger Bohr radius: stronger confinementlower deposition temperature has been proposed for next generation high transportchannel devices and nanodevices

Ge NW growth is now well assessed in IMEMAu nanoparticles as catalyst“novel” metal‐organic Ge precursor: Isobutyl GermaneWide range of growth conditions explored

Si NW growth is planned

Ge NW processing:sonication to detach NW from the substratesingle‐NW electrical characterizationchemical functionalization in progress

NATO Science for Peace – nanostructures for explosive detection

NATO Science for Peace – nanostructures for explosive detection

Single Ge NW, about 15 m long

Pt contact (FIB)

Metal contact pads

SiO2/Si substrate

resistivity ≈ 0.05‐0.07 Ωcm

Electrical characterization of single Ge NW

Uncapped QDs for molecular sensing: PL study and theoretical modeling

Sensing devices based on nanostructuresSensing of polar moleculesEfficiency + reliability + compactness

Nanostructures: uncapped InAs/GaAs QDsPL emission depends on the external environment (humid vs dry)

Uncapped QDs for molecular sensing: PL study and theoretical modeling

Intensity and emission energy of PL spectra change upon the exposure to humid environmentModeling: the cause are oxidation of uncapped QDs and passivation of surface states

Fabrication of 3D architectures by strain‐induced self‐rolling MBE bilayers

Sensing devices based on nanostructuresMicrofluidics channels for sensingNovel microtube‐based photonic integrated components

Highly ordered array of 3D‐objectsPrecise positioning (top‐down approach)Perfect single‐crystal qualityBilayer overgrowth with functional layers

Fabrication of 3D architectures by strain‐induced self‐rolling MBE bilayers

tube‐wall thickness control at the nm scale

lateral view

Sensing devices based on nanostructuresMicrofluidics channels for sensingNovel microtube‐based photonic integrated components

Novel oxide semiconductors

Gallium Oxide ‐ Ga2O3 researchA new material for very high power devices and deep‐UV detectors

IMEMPhysics dept. UniPR(+ national and international network of collaborators)

Ga2O3 key properties:bandgap: 4.7 – 4.9 eVbreakdown field: 8 MV cm‐1

Applications: Potentialities for device performances beyond GaN and SiC for 

very high power applications Solar blind UV‐detectors

Novel oxide semiconductors

Aims Basic material science to realize, characterize and understand a “new” compound Build test devices (electrical, optical sensors)

Critical issuesGa2O3 has several polymorphs:

most interesting: ‐Ga2O3 (stable, grown at 800‐900 °C)our phase, ‐Ga2O3, is metastable but still technologically relevant

We should upgrade the growth systemRealize test devicesStill no fundings despite several proposal submitted

Interest in Ga2O3 is increasing rapidly…

# of papers

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2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

Scopus: Ga2O3 in  title, abstract, keywords

Novel oxide semiconductors

pubblicazione citazioniHetero‐epitaxy of ε‐Ga2O3 layers by MOCVD and ALD giu‐16 35Crystal structure and ferroelectric properties of ϵ‐Ga2O3 films grown on (0001)‐sapphire nov‐16 29The real structure of ε‐Ga2O3 and its relation to κ‐phase feb‐17 20ε‐Ga2O3 epilayers as a material for solar‐blind UV photodetectors feb‐18 9Thermal stability of ε‐Ga2O3 polymorph nov‐17 7

Dedicated conference, workshop, focused sessions

Main drivers: Japan, USA (US‐Army), Germany

Solar‐blind UV Photodetectors

4.41 Ev3.92 Ev 6.18 Ev

Detection of weak UV radiation on vis‐IR backgrounds:• There is no terrestrial background at less than 280 nm (UVC)• Heat sources (flames, jet engines, or missile plumes) emit UVC

Easy detection of emitters at wavelengths less than 280 nm: “solar blind” UV detector

Applications: detect missile plume, airplane engines (security) flame monitoring in boiler control and fire‐safety equipment   UV exposure control in photolithographic and binder curing processes imaging of UV objects in astronomy UV sensing elements in advanced medical and biological instruments

‐Ga2O3 is suitable for detection of deep‐UV radiation • Very basic test device already proved

Novel oxide semiconductors

Bandgap of ‐Ga2O3 ~  4.6 eV (270 nm)

Silicon Carbide (3C‐SiC)for:  MEMS (Micro Electro Mechanical Systems)

Defects in 3C‐SiC as single photon sourcePower devices

VPE growth in hot‐wall reactor (up to 1400 °C) State of the art 3C‐SiC deposited on silicon substrates (2x4 cm2)n‐type dopingnational and international network of collaborators

Activity is now in standby: the reactor is used for NATO project nanowiresAims

A material useful for micro mechanical sensors A new platform for single photon emission and quantum optical structures

No more fundings. In the past (2015‐2018): about 60K € from a company to develop a 3C‐SiC epitaxial process for power devices

3C‐SiC

3C‐SiC

Optical microscope

Suspended 3C‐SiC/Si MEMS structures to be used as high‐sensitivity strain sensors  (e.g. engines)high T applications (up to 500 °C)ultra high‐resolution enhanced sensitivity with respect to standard Si design

IMM‐Bologna

3C‐SiC

A new platform for single photon emission and quantum optical structures

Collaboration with RMIT Melbourne, Australia

Single photon source (SPS):emits one photon at a timeat a time decided by the userwith adjustable repetitionhighly polarisedindistinguishable photons

Some defects in SiC can act as SPS, created by:implantation+annealoxidation 

3C‐SiC

SPS formation by 3C‐SiC  oxidation and anneal

Photon antibounching measurement 

3C‐SiC

Fabrication of optical disk resonator suspendedIMEM 3C‐SiC 

Si substrate

Integration of SPSinto a disk resonator

Confocal microscope used to probe signel defect and define a disk mask aligned accordingly

Single/entangled photon at telecom wavelengths by metamorphic InAs/InGaAs QDs

Metamorphic InAs/InGaAs QDs

Metamorphic InAs QDs by MBE

Thermally stimulated current:defect density in metamorphic QDs is comparable to standard In(Ga)As QDs

Photocurrent: a good photoresponsitivity in the C‐, S‐ and E‐bands is preserved in metamorphic QDs 

Metamorphic InAs/InGaAs QDs

Golovynskyi S, Datsenko O I, Seravalli L, Trevisi G, Frigeri P, Babichuk I S, Golovynska I and Qu J 2018 Nanoscale Research Letters 13 103

Golovynskyi S, Datsenko O I, Seravalli L, Trevisi G, Frigeri P, Babichuk I S, Golovynska I and Qu J 2019 Semiconductor Science and Technology (in press)

Single/entangled photon at telecom wavelengths by metamorphic InAs/InGaAs QDs

Scientific areas of interest:Strucutres tailored to sensing (nanowires, quantum dot, microtubes, MEMS)Power devicesPhotonics

Skills:Epitaxial growth (MOVPE, ALD, MBE)

Materials: Ge, Ga2O3, SiC, III‐VCharacterization of semiconductors and nanostructures:

Morphological (SEM, AFM)Structural (XRD)Optical (PL, transmission, reflectance)Electrical

Focused ion beam micro/nano fabricationphotolitographyDesign / modeling of quantum structures and photonics structures

Main facilities:2x MOVPEMBE for semiconductor epitaxyXRD systems (alta risoluzione, detector 2D)Photoluminescence, transmittance, reflectanceClean room for chemical preparation with laminar hoodElectrical characterizationTiberCAD software modelling

UdR “Growin” – in conclusione

UdR “Growin”

fine

3C‐SiC

NATO Science for Peace – nanostructures for explosive detection

The problem / main motivations Enhanced needs for security Detection of explosives (Improvised Explosive Devices) Safety of infrastructures (airports, railway stations, roads, buildings, …)

Current solutions Different technologies to detect threats (e.g. explosives)

mass spectroscopy  gas chromatography (GS) Laser Induced Breakdown Spectroscopy (LIBS) infrared absorption (IR) Raman spectroscopy (RS)  ….

Future needs Higher sensitivity Broad sensing Portable sensors with limited weight and power consumption No human intervention: unmanned exploration of dangerous sites

Overview &Milestones Synthesis of materials tailored for explosive detection

semiconducting nanowires: germanium, siliconcarbon nanotubes

Chemical functionalizationelectron‐rich amino‐silanecharge‐transfer donor‐acceptor interactions sharp changes in the conductance of the electrical‐sensing nanoelements

SensingTNT, Dinitrobenzene, Nitroamine , Nitrobenzene, 2‐Nitrotoluene, etc

Devicefunctionalized nanowires in FET configurationcurrent change in functionalized carbon nanotubes 

2018

2020

NATO Science for Peace – nanostructures for explosive detection

Overview &Milestones Synthesis of materials tailored for explosive detection

semiconducting nanowires: germanium, siliconcarbon nanotubes

Chemical functionalizationelectron‐rich amino‐silanecharge‐transfer donor‐acceptor interactions sharp changes in the conductance of the electrical‐sensing nanoelements

SensingTNT, Dinitrobenzene, Nitroamine , Nitrobenzene, 2‐Nitrotoluene, etc

Devicefunctionalized nanowires in FET configurationcurrent change in functionalized carbon nanotubes 

2018

2020

NATO Science for Peace – nanostructures for explosive detection